Work machines, particularly tractors for agriculture, construction, earthmoving, forestry, and other towing applications, have improved over the years, both as to comfort for the operator of the work machine, and as to stress and loads applied against the work machine itself and against trailers or implements towed thereby, particularly as the machine moves over rough or irregular terrain, and for increasing the efficiency of operation by allowing for increased operating speeds and less operator fatigue. In particular, it is known for a work machine or tractor to have an automatic or selectably variable suspension or ride control, to improve operator comfort and allow for faster over-ground speed. It is also known for a tractor to have a drawbar for towing trailers and implements, which is resiliently supported, and/or automatically variable in height, length and/or sideward position, for functions such as accommodating different trailers or implements, loading conditions, and shock absorption. Reference in this regard, Bernhardt et al. U.S. Pat. No. 6,698,524 entitled Implement Hitch and Control System which is automatically operable for controlling the length of coupling elements of the hitch as a function of sensed forces applied against the coupling elements and position of an implement towed by the hitch, for controlling parameters including the operating line of draft forces acting on the hitch, towing point position, and/or inclination of a towed implement.
However, it has been found that even with a controlled suspension and/or ride control, and an automatically controllable hitch or drawbar, the automatic hitch or drawbar control may not suit individual operator preferences, and/or may not provide sufficient adaptability, either manual or automatic, for accommodating changing load and/or other operating conditions, such as braking and/or gear shifts/clutch operation. For instance, a towed trailer or implement, particularly a heavy one, or one which exerts a heavy load on the towing tractor, or a varying load thereon, can exert different forces and loads in different ways on a drawbar and thus on the towing vehicle, such as a tractor, as a result of a variety of factors. As an example, a drawbar control mode may be well suited for travel over paved roads, such as for travel between fields, involving only infrequent or occasional stopping, slowing and turning, but may be less suited to travel over irregular terrain such as a cultivated field wherein the drawbar is subjected to frequent jerking or jarring. Conversely, a control mode suitable for travel over rough or irregular terrain may be less suited for travel over smooth roads. The wrong control mode for a hitch or drawbar can negatively affect ride quality, steering, stability, and handling of a tractor, and thus operator satisfaction.
Even when environmental conditions such as terrain are consistent, load conditions can vary widely over a relatively short time period, such as when a grain cart being towed by a tractor is being filled with grain by a combine, or a fertilizer spreader towed by a tractor is spreading fertilizer over a field. In this regard, a grain cart can be loaded within a few minutes with an amount of grain having a weight which is several times the weight of a tractor towing the cart, thereby greatly changing the load on the drawbar. A fertilizer spreader can carry a load of fertilizer having an initial weight which is also several times the weight of the tractor towing the spreader, but which is gradually reduced to a much lower weight over the course of the spreading operation, which will also change the drawbar load. Further, towed implements such as agricultural drills and planters will exert a varying load on the drawbar of the towing vehicle as disks, plows or other tools of the implement are lowered into and raised from the ground, or, while in the ground encounter changing soil conditions or buried obstructions such as roots and old fence posts.
Still further, operation of the towing vehicle itself, either alone, or in combination with any of the above factors, can result in changes in drawbar loading conditions. For instance, drawbar loads will change when the towing vehicle is braked, and/or the clutch is engaged and disengaged, such as when shifting gears.
As a result, it has been found that it would be desirable to have a control for a drawbar of a hitch of a work machine, such as a tractor, which provides different selectable operating modes suitable for a variety of different operating and/or load conditions, as well as operator preferences, which is optionally automatically adaptable for changing conditions, such as when the towing vehicle is braking and/or the clutch is engaged or disengaged, and which overcomes one or more of the problems and shortcomings set forth above.